The output characteristics of a conventional shift register is related to the polarity of TFTs constituting the shift register, that is, the shift register constituted by N-type TFTs outputs a high voltage Vgh in an operating period, and the shift register constituted by P-type TFTs outputs a low voltage Vgl in the operating period. Existing shift register fails to provide a low voltage output and a high voltage output simultaneously.
In a circuit of a pixel structure of Active Matrix Organic Light-Emitting Diode (AMOLED) having a compensation function, besides that a startup voltage is required to function as it is, another voltage inverse to the startup voltage is also required to function as another startup voltage. The compensated pixel structure constituted by P-type TFTs as shown in FIG. 1 requires five driving signals, wherein DATA (data) signal 11 and VDD (power supply) signal 14 are provided directly by a Source IC (driving circuit board), the other three signals are inputted to the pixel structure through a shift register, wherein the startup voltage for GATE (gate) signal 12 and for RESET (reset) signal 13 is a low voltage and the startup voltage for EMISSION (emission) signal 15 is a high voltage. Therefore, existing shift registers cannot satisfy the requirement of providing the GATE (gate) signal and the RESET (reset) signal as a low voltage and the EMISSION signal as a high voltage at the same time.